Managing Concurrent Data Access

Users who access a resource at the same time are said to be accessing the resource concurrently. Concurrent data access requires mechanisms to prevent adverse effects when multiple users try to modify resources that other users are actively using.

The concurrency control mechanisms fall into the following categories:

Optimistic concurrency control works to minimize reader/writer blocking. With optimistic concurrency control methods, read operations do not use read locks that block data modification operations.

Pessimistic concurrency control works to ensure that read operations access current data and that data being read cannot be modified. With pessimistic concurrency control methods, read operations use read locks that block data modification. The locks placed by a read operation are released when the read operation is finished.